The present invention relates to a no-fuel heating system making use of stored energy which may be of natural, e.g. solar or of man-made origin and be available at times when it is not required. Thus, solar insolation in the cold season is quite limited in most climates and accordingly collection of solar energy during the cold season for the production of sensible heat, e.g. for space heating, at that time would by conventional methods require collectors of a very large surface area. It is therefore desirable to store solar energy collected in the summer in large seasonal storage facilities to be used in winter for space heating. A similar problem may be encountered in power production in that available power stations may over-produce in summer so that it may become desirable to store the over-produced excessive energy to be avaiIable as sensible heat in winter.
Conventional seasonal heat storage facilities from which sensible heat is to be withdrawn in the winter are not satisfactory in that they have to be quite large and heat losses to the environment are unavoidable.